The present invention relates to a probe for use in measuring circuit parameters. More specifically, the invention concerns a high-frequency probe having active circuitry positioned near its signal contact needle.
Ideally, a measurement probe would not affect a measured circuit's performance, yet it would accurately provide the circuit's state to a measurement instrument. To achieve this, an ideal high-frequency probe would present an infinite input resistance and zero input capacitance to the circuit being measured. Although an actual probe will have a non-infinite input resistance and a non-zero input capacitance, its input characteristics may be improved using active circuitry positioned near its contact needles.
Typically, active probes use cantilevered contact pins for making electrical connection with a measured circuit. Such cantilevered pins have significant capacitance and dictate relatively long return ground paths. Furthermore, such cantilevered pins can hinder precise pin placement since an increase in the contact pressure can cause the pin to flex and thus displace laterally.
Telescoping pin probes overcome the repeatable positioning problems of cantilevered probes. One such probe is shown in Hadwin et al., U.S. Pat. No. 4,739,259. However, the probe of Hadwin has no active circuitry near its contact tip, nor does it provide a relatively short return ground path.
What is needed, then is a high-frequency probe which has a relatively high input resistance and minimal input capacitance and which provides a relatively short return ground path.